Saxon

I'm implementing some logic from XProc and want to round trip between JSON and XML using the java API only (not from within a stylesheet). I've got half of the task working, but the trip back causes an exception.

I've pasted a test class below. It was adapted from JsonToXMLFn and XMLToJsonFn and I've commented out some code related to options.

Going from JSON to XML works as expected, but converting XML to JSON causes an IllegalStateException in JsonReceiver.

Can someone help get this working? Any advice on how to improve the code in general would also be appreciated.

package saxon.demo;

import java.io.ByteArrayOutputStream; import java.nio.charset.StandardCharsets; import java.util.logging.Level; import java.util.logging.Logger;

import javax.xml.transform.dom.DOMSource;

import org.w3c.dom.Document; import org.w3c.dom.Element; import org.w3c.dom.Node;

import net.sf.saxon.Configuration; import net.sf.saxon.dom.NodeOverNodeInfo; import net.sf.saxon.event.PipelineConfiguration; import net.sf.saxon.expr.XPathContextMajor; import net.sf.saxon.expr.instruct.Executable; import net.sf.saxon.expr.parser.ExplicitLocation; import net.sf.saxon.ma.json.JsonHandlerXML; import net.sf.saxon.ma.json.JsonParser; import net.sf.saxon.ma.json.JsonReceiver; import net.sf.saxon.om.Item; import net.sf.saxon.s9api.DocumentBuilder; import net.sf.saxon.s9api.Processor; import net.sf.saxon.s9api.SaxonApiException; import net.sf.saxon.s9api.Serializer; import net.sf.saxon.s9api.XdmNode; import net.sf.saxon.trans.XPathException; import net.sf.saxon.tree.tiny.TinyDocumentImpl;

public class JsonXmlRoundTrip_main {

public static void main(String[] args) {
	
	Logger logger = Logger.getAnonymousLogger();
	
	String json = "{\"foo\":\"bar\"}";

	Element convertedElement = convertJsonToXml(json, logger);
	if (convertedElement == null) {
		return;
	}
	String markup = serializeToString(convertedElement, logger);
	System.out.println("convertedElement:");
	System.out.println(markup);

	String convertedJson = convertXmlToJson(convertedElement, logger);
	if (convertedJson == null) {
		return;
	}
	System.out.println("convertedJson:");
	System.out.println(convertedJson);

	System.out.println("compare json:");
	System.out.println(json.equals(convertedJson));
}

private static Element convertJsonToXml(String json, Logger logger) {
	
	//adapted from saxon JsonToXMLFn
	
    JsonParser parser = new JsonParser();
    int flags = 0;

// Map<String, Sequence> checkedOptions = null; // if (options != null) { // checkedOptions = getDetails().optionDetails.processSuppliedOptions(options, context); // flags = JsonParser.getFlags(checkedOptions, true, context.getController().getExecutable().isSchemaAware()); // if ((flags & JsonParser.DUPLICATES_LAST) != 0) { // throw new XPathException("json-to-xml: duplicates=use-last is not allowed", "FOJS0005"); // } // if ((flags & JsonParser.DUPLICATES_SPECIFIED) == 0) { // if ((flags & JsonParser.VALIDATE) != 0) { // flags |= JsonParser.DUPLICATES_REJECTED; // } else { // flags |= JsonParser.DUPLICATES_RETAINED; // } // } // } else { flags = JsonParser.DUPLICATES_RETAINED; // }

	Processor proc = new Processor(false);
	XPathContextMajor context = createDisposableXpathContext(proc);
    String baseUri = null;
	try {
		JsonHandlerXML handler = new JsonHandlerXML(context, baseUri, flags);

// if (options != null) { // handler.setFallbackFunction(checkedOptions, context); // } parser.parse(json, flags, handler, context); Item<?> resultItem = handler.getResult(); if (resultItem instanceof TinyDocumentImpl) { Node domNode = convertTinyDocToDom((TinyDocumentImpl)resultItem); if (domNode instanceof Document) { return ((Document)domNode).getDocumentElement(); } else if (domNode instanceof Element) { return (Element)domNode; } } logger.severe("unable to convert JSON to XML"); return null; } catch (XPathException e) { logger.log(Level.SEVERE, "an error occurred while converting JSON to XML", e); return null; } }

private static String convertXmlToJson(Node node, Logger logger) {
	
	//adapted from saxon XMLToJsonFn

	Processor proc = new Processor(false);
	XdmNode item = proc.newDocumentBuilder().wrap(node);
	XPathContextMajor context = createDisposableXpathContext(proc);
	PipelineConfiguration pipe = context.getController().makePipelineConfiguration();
    pipe.setXPathContext(context);
	JsonReceiver receiver = new JsonReceiver(pipe);
    receiver.setIndenting(true);

// if (options.numberFormatter != null) { // receiver.setNumberFormatter(options.numberFormatter); // } // Receiver r = receiver; // if (xml.getNodeKind() == Type.DOCUMENT) { // r = new DocumentValidator(r, "FOJS0006"); // }

    try {
    	receiver.open();
    	
    	//this causes IllegalStateException in JsonReceiver
		item.getUnderlyingNode().copy(
				receiver, 
				0, 
				new ExplicitLocation(null, -1, -1));
		
		receiver.close();
		return receiver.getJsonString();
	} catch (XPathException e) {
		logger.log(Level.SEVERE, "unable to convert XML to JSON", e);
		return null;
	}
}

private static XPathContextMajor createDisposableXpathContext(Processor proc) {
	
	Executable exec = new Executable(proc.getUnderlyingConfiguration());
	return new XPathContextMajor(null, exec);
}

private static String serializeToString(
		Node node,
		Logger logger) {
	
	Configuration config = new Configuration();
	Processor processor = new Processor(config);
	ByteArrayOutputStream baos = new ByteArrayOutputStream();
	Serializer serializer = processor.newSerializer(baos);
	boolean success = serialize(
			node, 
			processor.newDocumentBuilder(),
			serializer, 
			logger);
	if (success) {
		return new String(baos.toByteArray(), StandardCharsets.UTF_8);
	} else {
		return null;
	}
}

private static boolean serialize(
		Node node,
		DocumentBuilder docBldr,
		Serializer serializer,
		Logger logger) {
	
	try {
		XdmNode xdmNode = docBldr.build(new DOMSource(node));
		serializer.setOutputProperty(Serializer.Property.INDENT, "yes");
		serializer.setOutputProperty(Serializer.Property.OMIT_XML_DECLARATION, "yes");
		serializer.setOutputProperty(Serializer.Property.ENCODING, "UTF-8");
		serializer.serializeNode(xdmNode);
		return true;
	} catch (SaxonApiException e) {
		logger.log(Level.SEVERE, "an error occurred while saving data", e);
		return false;
	}
}

private static Node convertTinyDocToDom(TinyDocumentImpl tinyDoc) {
	
	//saxon no longer implements w3 dom in TinyTree, so NodeOverNodeInfo
	//provides a read-only w3 dom api over tiny node
	//https://www.saxonica.com/documentation9.5/changes/v8.3/external-object-models.html
	return NodeOverNodeInfo.wrap(tinyDoc.getRootNode());
}

}